Liquid-metal-cooled reactor

ABSTRACT

A liquid-metal-cooled reactor comprising two rotatable plugs, one of them, having at least one hole, being arranged internally of the other, a recharging mechanism with a guide tube adapted to be moved through the hole of the first plug by means of a drive, and a device for detecting stacks with leaky fuel elements, the recharging mechanism tube serving as a sampler.

The present invention relates to nuclear engineering, and moreparticularly to a liquid-metal-cooled reactor.

Known in the art are liquid-metal-cooled reactors comprising tworotatable plugs, the first plug having at least one hole and beingarranged internally of the second, a recharging mechanism with a guidetube adapted to move through the hole of the first plug with the aid ofa drive and accommodating a rod provided with means for gripping a fuelelement stack and removing it from the reactor core into the guide tube.These reactors are also provided with a device for detecting stacks withleaky fuel elements, comprising a sampler to withdraw coolant samplesfrom each individual fuel element stack, with an inert carrier gas beingfed under pressure to the sampler, and having an inner space wherein acoolant sample is degassed and which communicates with a device formeasuring the radioactivity of the inert carrier gas and of the gasesevolved from the coolant sample, evacuated from the sampler.

A disadvantage inherent in such a liquid-metal-cooled reactor,comprising a device for detecting stacks with leaky fuel elementsresides in the complexity of the design of the sampler of the device fordetecting stacks with leaky fuel elements, which sampler is made in theform of a collector with intricate piping arranged inside the reactor.This complicates the recharging of the fuel element stacks, whichinvolves dismantling of the whole installation. The reactor is thusrendered difficult to operate, with additional time required to checkfaulty fuel element stacks, and the risk of exposure to radioactivematter contaminating the equipment inside the reactor involved.

It is an object of the invention to provide a liquid-metal-cooledreactor allowing consecutive checks of all fuel element stacks withoutremoving them from the reactor core, upon stopping the reactor, and, atthe same time, to remove faulty stacks from the core.

With this and other objects in view, the present invention relates to aliquid-metal-cooled reactor comprising two rotatable plugs, one plughaving at least one hole and being arranged internally of the other, arecharging mechanism with a guide tube for moving through the hole ofthe first plug and accommodating a rod with means for gripping a fuelelement stack and removing it from the core into the guide tube, and adevice for detecting stacks with leaky fuel elements, provided with asampler to withdraw coolant samples from individual fuel elements, whichsampler is adapted to receive inert carrier gas fed thereto underpressure and to degas a coolant sample, the inner space of the samplercommunicating with means for measuring the radioactivity of the inertcarrier gas and of the gases evolved from the coolant sample, bothevacuated from the sampler.

According to the invention, the guide tube of the recharging mechanismis used as the sampler, together with means for introducing the inertcarrier gas, and means for evacuating the inert carrier gas togetherwith the gases evolved from the coolant sample.

It is recommended that the wall of the guide tube of the rechargingmechanism be provided with a duct for removing the inert carrier gastogether with the gases evolved from the coolant sample, which ductcommunicates with the inner space of the guide tube through a hole madein the guide tube wall, above the coolant level, and a duct for feedingthe inert carrier gas into the tube, which duct also communicates withthe inner space of the guide tube through a hole made in the that wall,level with the bottom end of the fuel element stack, transferred fromthe core to the tube.

It is alternatively also suggested that a duct be provided in the wallof the rod with the gripper for feeding the inert carrier gas into thetube, which duct communicates with the inner space of the rod through ahole in the proximity to the end face of the rod, fitted on the bottomend whereof is a sealing member intended to shut off the coolant flowfrom the fuel element stack, as well as at least one hole made in therod above the coolant level in the guide tube to evacuate the inertcarrier gas together with the gases evolved from the coolant sample.

Other objects, advantages and features of the invention will becomeevident from the following description of preferred embodiments thereoftaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an elevational view of a liquid-metal-cooled reactor,according to the invention; and

FIG. 2 is an elevational view of another embodiment of theliquid-metal-cooled reactor, according to the invention.

Referring now to FIG. 1, the inventive liquid-metal-cooled reactor 1comprises two rotatable plugs 2 and 3, one of them /plug 2/ beingarranged in the other /plug 3/ and having a hole 4. The plug 2 may beprovided with additional holes. The reactor 1 also comprises a housing5, a cover /not shown/, a core with fuel element stacks 6 washed by acoolant 7, and a recharging mechanism 8 with a guide tube 10 adapted tomove through the hole 4 of the rotating plug 2 with the aid of a plug 9.The guide tube 10 accommodates a rod 11 with a gripper 12 for grippingthe stack 6 and removing it from the core into the guide tube 10.

The reactor 1 further comprises a device for detecting stacks 6 withleaky fuel elements. The guide tube 10 serves as a sampler in thedetecting device, which makes for consecutive sampling of the coolantfrom each stack 6. Provided in the wall of the guide tube 10 is a duct13 for feeding an inert carrier gas into the sampler which ductcommunicates with the inner space of the guide tube 10 through a hole 14made in the wall of the tube 10 level with the bottom end 15 of thestack 6 transferred from the core of the reactor 1 into the tube 10.

The duct 13 for feeding the inert carrier gas also communicates with adoser 16 of a known design through a pipe 17. A duct 18 for evacuatingthe inert carrier gas together with the gases evolved from a coolantsample from the sampler is provided in the wall of the guide tube 10 andcommunicates with the inner space thereof through a hole 19 made in thewall of the tube 10 above level B of the coolant 7 in the tube 10 /C isthe coolant level in the vessel of the reactor 1/. The other outlet ofthe duct communicates through a pipe 20 with means 21 for measuring theradioactivity of the outgoing gases, preferably in the form of aconventional instrument for measuring the concentration of a radioactivegas.

Turning now to FIG. 2, the modified inventive reactor 22, as compared tothe reactor 1 of FIG. 1, comprises a duct 23 for feeding the inertcarrier gas provided in the wall of the rod 11 and communicating withthe inner space thereof through a hole 24 made in proximity to the endface of the rod 11. Fitted on the bottom end of the latter is a sealingmember 25 shutting off the coolant flow from the stack 6. Made above thecoolant level B in the tube 10, in the wall of the rod 11, are aplurality of holes 26 through which the inner space of the rod 11communicates with the hole 19 in the guide tube 10 to direct the inertcarrier gas together with the accumulated gas through the duct 18 andthe pipe 20 to the means 21 for measuring the radioactivity of the gas.

The liquid-metal-cooled reactor provided with a device for detectingstacks with leaky fuel elements operates as follows. The detection ofstacks with leaky fuel elements during the recharging of fuel elementstacks is ensured by the structure of the liquid-metal-cooled reactor 1shown in FIG. 1. The tube 10 of the recharging mechanism 8 ispositioned, by means of the rotatable plugs 2 and 3, above the fuelelement stack 6, then lowered by means of the drive 9 towards the cap ofthe stack 6. The gripper 12 grips the cap and, as the rod 11 is movedup, the stack 6 is introduced into the tube 10. The inert carrier gas isfed under a pressure exceeding that of the coolant 7 from the doser 16through the pipe 17 and duct 13 into the inner space of the tube 10containing the coolant 7. The inert carrier gas makes the coolant 7bubble in the space, thus degassing it and entraining the radioactivegases from leaky fuel elements of the stack 6. Then, the gas mixturepasses through the hole 19, duct 18 and pipe 20 to the measuring means21.

To avoid introducing the stack 6 into the tube 10, use should preferablybe made of a reactor embodied as shown in FIG. 2. The tube 10 ispositioned, by means of the plugs 2 and 3, above the stack 6 beingcontrolled, and the rod 11 is lowered, by means of the drive /not shown/until the rod is tightly fitted on the stack 6 by means of the sealingmember 25. The inert carrier gas is fed under a pressure exceeding thatof the coolant 7 from the doser 16 through the pipe 17 and duct 23 intothe inner space of the guide tube 10, the pressure of the inert carriergas being sufficient to maintain the level B of the coolant 7 in thetube 10.

After the accumulation of gases in the inner space of the tube, thepressure of the inert carrier gas is brought down, the coolant isbubbled and the accumulated radioactive gas is evacuated. Then, theinert carrier gas together with the radioactive gases evolved from thesample of the coolant 7 are also delivered to the measuring means 21through the inner space of the rod 11, holes 26 and 19, duct 18 and pipe20.

If the measuring means 21 indicates that the concentration ofradioactivity has reached a critical level, the stack 6 is removed fromthe core of the reactor 22. To do this, the rod 11 is lifted by means ofits drive, the tip 25 is detached from the stack 6, the gripper 12 ismade to grip the cap of the stack 6, and the rod 11 together with thegriper 12 and the stack 6 are directed into the guide tube 10 to beextracted from the reactor 22.

The inventive reactor with a device for detecting stacks with leaky fuelelements permits of consecutive checks, upon stopping the reactor, ofall stacks with the ultimate aim of locating stacks with leaky fuelelements without removing them from the reactor core, as well as easyextraction (with the aid of conventional means and devices) of thefaulty stacks from the reactor.

If necessary, the stacks may be checked at the same time with theirrecharging, both when the coolant is stationary and when circulated byforce.

Thus, the time required to shut down the reactor to locate stacks withleaky fuel elements is minimized, thereby allowing considerable savingsto be made.

By applying the present invention to a reactor known as the type BR-5,it has become possible to reduce the shut-down time required to check afuel element stack to one hour /from six hours with the oldconstruction/, and in the case of another reactor, known under thedesignation BOR-60, to half an hour. Moreover, this method of detectingfaulty stacks has proved highly reliable /in the case of the latterreactor type, not a single faulty stack was missed even though a singlemeasurement was taken/.

The present invention assures total reactor and personnel safety.

What is claimed is:
 1. A liquid-metal-cooled reactor comprising: ahousing; a core in said housing; fuel elements in said core; stacks ofsaid fuel elements in said core; a first rotatable plug having at leastone hole; a second rotatable plug disposed in said housing andaccommodating said first plug; a recharging mechanism; a drive in saidrecharging mechanism; a guide tube in said recharging mechanism formoving through said hole along the longitudinal axis of the reactor withthe aid of said drive; a rod inside said guide tube, having an innerspace, for gripping the fuel-element stacks and remove them from saidcore into said guide tube; a gripper in said inner space of the latter;a device for detecting stacks with leaky fuel elements; said guide tubealso serving as a sampler in said detecting device; said sampler havingan inner space for receiving inert carrier gas fed under pressurethereto and to degas a coolant sample; means inside said guide tube forintroducing the carrier gas into said sampler; means inside said guidetube for evacuating the gas together with gases evolved from the coolantsample; and means for measuring the radioactivity of the carrier gastogether with that of the evolved gases, both removed from said sampler,and communicating with said inner space of the latter.
 2. The reactor asdefined in claim 1, wherein said introducing means is in the form of afirst duct in a wall of said guide tube, communicating with said innerspace of the guide tube through a first hole made in said wall below thelevel of the bottom end of the stack, transferred from said core intosaid guide tube; and wherein said evacuating means is in the form of asecond duct in said wall, communicating with said inner space of theguide tube through a second hole made in said wall above the level ofthe coolant sample in said guide tube.
 3. The reactor as defined inclaim 1, wherein said introducing means is in the form of a first ductin a wall of said rod, communicating with said inner space of the rodthrough a hole made in the proximity to an end face of said rod; asealing member for shutting off the flow of the coolant sample from thestack on said end face of the rod; said evacuating means is in the formof a second duct in a wall of said guide tube, communicating with saidinner space of the latter; and wherein said wall of the rod has thereinanother hole above the level of the coolant sample in said guide tube.